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Old 05-13-2004, 03:20 PM   #1
RS25Tuner
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Question Blow off valve question

Can I feed the escaping air from my blow off valve back into my intake to stop my car from stalling out? The stalling problem only occurs when I put the clutch in to slow down or to coast after being at a high rpm. (i.e. above 4000 rpm) I have attached a picture of my blow off valve. I have also been told I that I donít want to dump the air back into my system in a 90 degree angle. I was told I want to point the air from the blow off valve in the direction of incoming air to blow directly into the intercooler to prevent the air from crossing my MAF sensor. I am currently using an Atmospheric blow off valve. I have attached the picture below to help illustrate my question.

Thanks RS25Tuner

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Old 05-13-2004, 03:28 PM   #2
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yes, that's how it should be set up. any open ports there after the MAF will cause your car to do this... plug them up, or put a hose on them asap.
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Old 05-13-2004, 03:30 PM   #3
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Aphex - Would you happen to have any pictures of modes like this I can reference?
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Old 05-13-2004, 03:31 PM   #4
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Yep, having that open could definately cause it to stall. The other option is using something like the decel air function on an SAFC. But with your configuration I would just route it back in, even if it's at a 90 degree angle. Mine was routed back in at about a 90 degree angle and about 3" downstream from the MAF and I never had any problems with it. From that picture it looks like you have a nipple on your intake directly across from the BOV. I would use that.

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Old 05-13-2004, 04:08 PM   #5
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Mancini - Would it be advices to feed compressed air into the uncompressed side of the air intake going into the turbo? This wouldnít cause a boost surge that could be a potential problem?
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Old 05-13-2004, 04:54 PM   #6
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when you are venting the air it decompresses, so if you vent back into your intake it should just be like it would draw it in anyways. if it is still somewhat compressed i dont think it would matter anyways, i would think the compressor just has to work less hard to compress it then

like i said im not positive on that but it seems logical to me.

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Old 05-13-2004, 05:52 PM   #7
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PHATsuby - Thanks for you advice... Can you just attach a hose to the bottom of the BOV and then attach it to the side nipple on my intake?
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Old 05-13-2004, 06:05 PM   #8
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no problem,

yea you could definitely do that.

i am assuming that black round section sticking out is what you are referring to?

if i were you i would drill that hole out, so that it is almost, if not the same diameter as your BOV vent, that way it will not be restricted, if it cant vent fast enough then you will get some compressor surge, so make that as large as possible.


hope this helps.

Ben
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Old 05-13-2004, 06:21 PM   #9
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PHATsuby- Makes sense.. I will need to think about the best way to approach this mod so I dont have to end up buying replacements.... From what it looks like I might not be able to match the diameter exactly... hmmm....
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Old 05-13-2004, 06:30 PM   #10
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dont worry about it being exact, just close, i mean anything larger than what it is right now will be an improvement

what purpose is that little extension on the intake serving now anyways?

Ben
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Old 05-13-2004, 06:39 PM   #11
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To my knowledge nothing.. it is just there for you if you want to use that option. I am still learning about this car. I have only owned it for about two months now and I am just starting to learn all the in's and out's of the thing.
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Old 05-13-2004, 09:39 PM   #12
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I'm just going to throw this suggestion out there:

Have you trried adjusting the BOV tension? Maybe it's too loose right now and it's letting too much air out. When I first put mine on, it was too loose, and it would stall on me during coasting....
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Old 05-13-2004, 11:00 PM   #13
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i think it has to do something with the MAF already accounting for that air that is being vented to atmosphere but i am not sure cause i dont have a MAF car.


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Old 05-13-2004, 11:05 PM   #14
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leondal - very good point... I haven't had this car very long and I haven't really looked at that feature yet. Plus this is my first Tuner...so I am still learning. How did you go about setting / adjusting your BOV to get it to keep from stalling?
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Old 05-13-2004, 11:31 PM   #15
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Well, I have a TurboXS blow-off valve, and those are adjusted using spacing washers that you put in the piston of the valve to increase spring tension. My BOV vents to the amotsphere 100%, and it didn't stall or have idle issues AT ALL after i tightened it.

Most aftermarket BOV have the ability to adjust tension, and I'm going to assume that most of them are loose for the 2.5 engine until you tighten them.

I don't know about your specific BOV, though.There's gotta be a way to do it though....Just don't tighten it too much, or else you'll start getting compression surge. You can tell compression surge by a "butterfly wing" flutter sound when you shift.
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Old 05-14-2004, 12:20 AM   #16
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I'm in a '98 MAF car with a heinous amount of boost. Recirculating the BOV is the only way to go. The S-AFC's decel function doesn't respond fast enough or with enough correction to matter. The air that has been dumped from the BOV to atmosphere has already been metered, but never reaches the cylinders. This results in 10x as much fuel being dumped as needed and will run your car rich enough to stall the motor almost instantly, not to mention really fould up your plugs, o2 sensors, cats, etc. Don't mess with your BOV tension. You want it to dump as much air as the thing is physically capable of without triggering under WOT boost conditions.

From those pictures it looks like it'll be really easy to dump the BOV back into that extra fitting on your intake.
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Old 05-14-2004, 08:59 AM   #17
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no-coast-punk - Thanks for the tip. I am having problems with my plugs getting fouled up. This could be exactly why. One thing I have been told by several people is to make sure that I donít vent the bov back into the intake at the 90-degree angle that is currently set up on my intake pipe. I was told to reposition the nipple at a 35-degree angle pointing at the turbo so that the air will not be measured twice by my MAF.

Are you running the 2.5 DOHC stock motor now?
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Old 05-14-2004, 02:12 PM   #18
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Sorry I didn't respond sooner but the above responses pretty much cover everything. When I was running my 98 RS-T I had a stock DSM/WRX bov, TurboXS Type H, and finally a HKS SSQV. I had the DSM bov venting back to the intake at probably a 90 degree angle and it worked awesome. I had no drivability problems at all. When I switched my intercooler setup I went with a TurboXS and I was having drivability issues with it. I couldn't get it tight enough to stay closed at idle and when I'd tighten it down I would get bad surge. That's why I switched to the HKS. It worked decently. Not stalling issues at all with dec air function on the SAFC because it was staying closed at idle. But I had very light surge when I let off at part throttle.

So what's all that mean, personally I like the stock BOV because it's slightly open at idle. This gives a fast response and helps prevent surge. The only problem is that a MAF based car needs to have this recirculated at all times or else it will be sucking in air at idle or light throttle. With an after market bov, if you aren't getting surge and don't feel any air getting sucked in at idle then the decel air function in an SAFC should solve your problems. If you feel air getting sucked in at idle you need to tighten the adjustment on the BOV so it stays shut. If you don't have an SAFC or something to adjust for the BOV then you'll need to plumb it back into the intake. Even if it's at a 90 degree angle it's still better than nothing...and you'll still probably have better reliability than before. Personally I'd plumb it back in and see how it works. Then go from there if it's still not running how you like.
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Old 05-14-2004, 03:26 PM   #19
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Mancini - Good idea. I guess it wont hurt to try it first at 90-degrees. If I start having drivablity issues I can then cut the nipple off and have it welded back on at a 35-degree angle and try it then to keep the air for hitting the MAF when it recirculates.
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